Which Pyrenean pass was the site of Charlemagne's 778 rear-guard ambush?

The 778 rear-guard ambush associated with Charlemagne took place at Roncevaux Pass in the Pyrenees. The pass lies in present-day Navarre, near the modern border between France and Spain, and formed part of an important route across the mountains.

After Charlemagne's unsuccessful campaign in Iberia, his army retreated toward Francia. As the long column crossed the narrow mountain route, Basque forces used the wooded, elevated terrain to attack the rear guard and baggage train. The isolated Frankish soldiers were overwhelmed, and several prominent figures died, including Roland, the governor of the Breton March, according to Charlemagne's biographer Einhard.

The historical attack was probably a relatively small mountain ambush, but later literature transformed it into a heroic battle between Christians and Muslims. The 11th-century Song of Roland greatly expanded Roland's role and introduced legendary details. The pass is also associated with a separate battle in 824, so the year matters: this question refers to the first, 778 engagement.